Aljuhani Maha A, Pelletier Jérémie D A, Basset Jean-Marie
KAUST Catalysis Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST).
KAUST Catalysis Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST);
J Vis Exp. 2019 Oct 18(152). doi: 10.3791/59409.
With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(≡Si-O-)Hf(=NMe)(η-NMe2)] is designed and prepared according to the methodology developed by surface organometallic chemistry (SOMC). In this framework, catalytic cycles can be determined by isolating crucial intermediates. All air-sensitive materials are handled under inert atmosphere (using gloveboxes or a Schlenk line) or high vacuum lines (HVLs, <10 mbar). The preparation of SiO2-700 (silica dehydroxylated at 700 °C) and subsequent applications (the grafting of complexes and catalytic runs) requires the use of HVLs and double-Schlenk techniques. Several well-known characterization methods are used, such as Fourier-transform infrared spectroscopy (FTIR), elemental microanalysis, solid-state nuclear magnetic resonance spectroscopy (SSNMR), and state-of-the-art dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS). FTIR and elemental microanalysis permit scientists to establish the grafting and its stoichiometry. H and C SSNMR allows the structural determination of the hydrocarbon ligands coordination sphere. DNP SENS is an emerging powerful technique in solid characterization for the detection of poorly sensitive nuclei (N, in our case). SiO2-700 is treated with about one equivalent of the metal precursor compared to the amount of surface silanol (0.30 mmol·g) in pentane at room temperature. Then, volatiles are removed, and the powder samples are dried under dynamic high vacuum to afford the desired materials [(≡Si-O-)Hf(ηπ-MeNCH2)(η-NMe2)(η-HNMe2)]. After a thermal treatment under high vacuum, the grafted complex is converted into metal imido silica complex [(≡Si-O-)Hf(=NMe)(η-NMe2)]. [(≡Si-O-)Hf(=NMe)(η-NMe2)] effectively promotes the metathesis of imines, using the combination of two imine substrates, N-(4-phenylbenzylidene)benzylamine, or N-(4-fluorobenzylidene)-4-fluoroaniline, with N-benzylidenetert-butylamine as substrates. A significantly lower conversion is observed with the blank runs; thus, the presence of the imido group in [(≡Si-O-)Hf(=NMe)(η-NMe2)] is correlated to the catalytic performance.
通过该方案，依据表面有机金属化学（SOMC）开发的方法设计并制备了一种定义明确的单中心二氧化硅负载的多相催化剂[(≡Si - O -)Hf(=NMe)(η - NMe₂)]。在此框架下，可通过分离关键中间体来确定催化循环。所有对空气敏感的材料都在惰性气氛（使用手套箱或施伦克线）或高真空线（HVLs，<10 mbar）下处理。SiO₂ - 700（在700℃脱羟基的二氧化硅）的制备及其后续应用（配合物的接枝和催化反应）需要使用HVLs和双施伦克技术。使用了几种知名的表征方法，如傅里叶变换红外光谱（FTIR）、元素微量分析、固态核磁共振光谱（SSNMR）以及最先进的动态核极化表面增强核磁共振光谱（DNP - SENS）。FTIR和元素微量分析使科学家能够确定接枝及其化学计量。H和C SSNMR可用于确定烃类配体配位球的结构。DNP SENS是一种新兴的强大的固体表征技术，用于检测低灵敏度核（在我们的案例中为N）。在室温下，将SiO₂ - 700与戊烷中约一当量的金属前体（相对于表面硅醇的量（0.30 mmol·g））进行处理。然后，除去挥发物，将粉末样品在动态高真空下干燥，得到所需材料[(≡Si - O -)Hf(ηπ - MeNCH₂)(η - NMe₂)(η - HNMe₂)]。在高真空下进行热处理后，接枝的配合物转化为金属亚胺基二氧化硅配合物[(≡Si - O -)Hf(=NMe)(η - NMe₂)]。[(≡Si - O -)Hf(=NMe)(η - NMe₂)]使用两种亚胺底物（N -（4 - 苯基亚苄基）苄胺或N -（4 - 氟亚苄基）- 4 - 氟苯胺）与N - 亚苄基叔丁胺的组合有效地促进了亚胺的复分解反应。空白实验观察到的转化率明显较低；因此，[(≡Si - O -)Hf(=NMe)(η - NMe₂)]中亚胺基的存在与催化性能相关。
